Heretofore, an infrared reflecting substrate having an infrared reflecting layer on a substrate of glass, film or the like is known. As the infrared reflecting layer, a metal layer such as silver is widely used from the viewpoint of enhancing the selective reflectivity of infrared rays. In an infrared reflecting substrate, a configuration in which a metal layer serving as an infrared reflecting layer and a metal oxide layer are alternately stacked is widely adopted to allow wavelength-selective transmission of visible light. In an infrared reflecting film using a film substrate, a transparent protective layer (top coat layer) made of resin is disposed on the surface of the infrared reflecting layer at a side opposite to the substrate, for the purpose of chemically protecting these metal layers and metal oxide layers.
In the infrared reflecting substrate, the metal layer of silver or the like reflects near-infrared rays such as solar light to impart heat shielding properties. On the other hand, in order to allow the infrared reflecting substrate to have heat insulating properties, it is important to reduce the emittance and to reflect far-infrared rays to the interior of a room by the infrared reflecting layer. Since a resin layer (organic material) used as the transparent protective layer of the infrared reflecting layer generally contains C═C bonds, C═O bonds, C—O bonds or aromatic rings, infrared vibration absorption of a far-infrared ray region of a wavelength of 5 μm to 25 μm is large. The far-infrared ray absorbed at the resin layer is dissipated outdoors as heat due to thermal conduction without being reflected at the metal layer. Therefore, when an amount of the far-infrared rays absorbed by the protective layer is large, the emittance is increased and the heat insulating effect is not achieved.
For the purpose of reducing the emittance of the infrared reflecting film, Patent Document 1 proposes reduction of far-infrared ray absorption caused by the protective layer with using a protective layer made of an Si-based material such as polysilazane, fluoroalkylsilane, or fluorosilane and setting the thickness thereof to be 500 nm or less. On the other hand, when the thickness of the protective layer is reduced, a chemical protecting effect on the infrared reflecting layer tends to decrease thereby leading to decrease in the durability of the infrared reflecting layer. In particular, silver is low in durability against oxygen, moisture, chlorine, and the like, so that, when an infrared reflecting layer mainly made of silver is degraded, the emittance of the infrared reflecting film tends to rise (the heat insulating properties decrease).
For this reason, Patent Document 1 proposes to improve the durability of the infrared reflecting layer by adopting a configuration in which the infrared reflecting layer made of a metal such as silver is interposed between metal layers having a high durability such as a Ni—Cr alloy.